Motion control system for vehicle

ABSTRACT

In a control unit of an own vehicle, specifically in a deceleration judging section, a deceleration calculating section and a brake control section, in order to avoid contacting an obstacle in front of the vehicle, the vehicle is automatically braked based on an distance between the vehicle and the obstacle, a vehicle speed and a road gradient. When a braking distance judging section judges that the vehicle can not avoid a contact with the obstacle with a deceleration presently applied, a first yaw rate calculating section calculates a first yaw rate necessary to avoid a contact with the obstacle and a second yaw rate calculating section calculates a second yaw rate presently generating. Further, a target yaw rate establishing section compares an absolute value of the first yaw rate with an absolute value of the second yaw rate and establishes a larger one of these values as a target yaw rate. Finally, an automatic brake control section calculates a target braking force at least based on the target yaw rate and selects an object wheel to be braked. As a result, the vehicle takes an avoidance motion so as to turn around the obstacle.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the invention

[0002] The present invention relates to a motion control system for avehicle and more particularly to a motion control system capable ofavoiding a contact with an obstacle by turning around the obstacle.

[0003] 2. Prior art

[0004] In recent years, in order to avoid collisions with obstaclesahead of an own vehicle, an automatic brake control system in which thedistance between the own vehicle and an obstacle is detected based onimages taken by a stereoscopic camera or a laser-beam radar and when thedistance is smaller than a predetermined value brake is appliedautomatically has been developed.

[0005] For example, Japanese Patent Application Laid-open No.Toku-Kai-Hei 7-149193 discloses a technique in which when the distancebetween detected by an inter-vehicle distance detecting apparatus issmaller than a calculated safe distance, an automatic brake is operated.In this technique, the safe distance is calculated taking a maximumdeceleration which the vehicle can generate according to the conditionof tires of respective wheels, road gradients and the like intoconsideration.

[0006] The technique for preventing collisions with obstacles is largelydependant upon how to calculate a deceleration of the vehicle. Sincethere are many factors affecting the deceleration of the vehicle, it isdifficult to take all of these factors into consideration and thereforethere is no assurance that the vehicle can stop before an obstacle.Further, an extreme deceleration is not preferable.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide a motioncontrol system capable of surely avoiding a contact with an obstaclelocated at the front of an own vehicle by turning.

[0008] In order to attain the object, a motion control system includingan obstacle recognition means for detecting an obstacle in front of thevehicle and for obtaining an information of the obstacle and a runningcondition detecting means for detecting running conditions of thevehicle, comprises a braking distance judging means for when adeceleration is applied to the vehicle judging whether or not thevehicle can finish the deceleration without contacting the obstaclebased on the information of the obstacle and the running conditions, afirst parameter calculating means for calculating a first parameternecessary to take a lateral avoidance motion based on the obstacleinformation and the running conditions, a second parameter calculatingmeans for calculating a second parameter representing a parameterpresently generating in the vehicle based on the running conditions, atarget parameter establishing means for when it is judged that thevehicle can not finish the deceleration without contacting the obstacle,establishing a target parameter by comparing the first parameter withthe second parameter and a vehicle behavior control means for generatingthe lateral avoidance motion of the vehicle at least in accordance withthe target parameter.

DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a functional block diagram showing a vehicle motioncontrol system according to a first embodiment of the present invention;

[0010]FIG. 2 is an explanatory view showing an overall schematicconstruction of a vehicle motion control system according to the firstembodiment;

[0011]FIG. 3 is a flowchart of a vehicle motion control system;

[0012]FIG. 4 is a functional block diagram showing a vehicle motioncontrol system according to a second embodiment of the presentinvention;

[0013]FIG. 5 is an explanatory view showing an overall schematicconstruction of a vehicle motion control system according to the secondembodiment;

[0014]FIG. 6 is a functional block diagram showing a vehicle motioncontrol system according to a third embodiment of the present invention;and

[0015]FIG. 7 is an explanatory view showing an overall schematicconstruction of a vehicle motion control system according to the thirdembodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0016] Referring now to FIG. 2, reference numeral 1 denotes a brakedrive section of a vehicle, to which a brake pedal 2 is connectedthrough a master cylinder 3. When a driver operates the brake pedal 2,the master cylinder generate a brake pressure and distributes the brakepressure to respective wheel cylinders 5(left front wheel cylinder 5_(fl), right front wheel cylinder 5 _(fr), left rear wheel cylinder 5_(rl) and right rear wheel cylinder 5 _(rr)) of four wheels (left frontwheel 4 _(fl), right front wheel 4 _(fr), left rear wheel 4 _(rl) andright rear wheel 4 _(rr)), thereby brake is applied to four wheels andthe vehicle is braked.

[0017] The brake drive section 1 is a hydraulic unit constituted by apressure generating source, a pressure reducing valve, a pressureamplifying valve and the like and can feed a brake pressure to therespective wheel cylinders 5 _(fl), 5 _(fr), 5 _(rl) and 5 _(rr)independently.

[0018] The wheel speed of the wheels 4 _(fl),4 _(fr), 4 _(rl) and 4_(rr) is detected by wheel speed sensors, a left front wheel speedsensor 6 _(fl), a right front wheel speed sensor 6 _(fr), a left rearwheel speed sensor 6 _(rl) and a right rear wheel speed sensor 6 _(rr),respectively. Further, a steering column of a steering wheel is providedwith a steering angle sensor 7. Further, the vehicle has a longitudinalacceleration sensor 8 for detecting a longitudinal acceleration of thevehicle, a lateral acceleration sensor 9 for detecting a lateralacceleration of the vehicle and a yaw rate sensor 10 for detecting a yawrate of the vehicle.

[0019] Signals from the wheel speed sensors 6, the steering wheel sensor7, the longitudinal acceleration sensor 8, the lateral accelerationsensor 9 and the yaw rate sensor 10, are inputted to a control unit 15.

[0020] Further, a pair of CCD cameras using a charge coupled device(CCD) are installed on the front part of a ceiling of a passengercompartment at a specified lateral interval and is connected with thecontrol unit 15.

[0021] The control unit 15 is composed of a vehicle speed calculatingsection 15 a, an obstacle recognition section 15 b, a decelerationjudging section 15 c, a deceleration calculating section 15 d, a brakecontrol section 15 e, a braking distance judging section 15 f, a firstyaw rate calculating section 15 g, a second yaw rate calculating section15 h, a target yaw rate establishing section 15 f and an automatic brakecontrol section 15 j.

[0022] The vehicle speed calculating section 15 a calculates a vehiclespeed V using the wheel speeds of the respective wheels detected by thewheel speed sensor 6 and the calculated vehicle speed V is outputted tothe obstacle recognition section 15 b, the deceleration judging section15 c, the deceleration calculating section 15 d, the braking distancejudging section 15 f, the first yaw rate calculating section 15 g, thesecond yaw rate calculating section 15 h and the automatic brake controlsection 15 j. The wheel speed sensor 6, the vehicle speed calculatingsection 15 a, the steering angle sensor 7, the longitudinal accelerationsensor 8, the lateral acceleration sensor 9 and the yaw rate sensor 10form a running condition detecting means.

[0023] The obstacle recognition section 15 b calculates distanceinformation over an entire image of a pair of stereoscopic picturestaken by the CCD cameras 11 from a deviation amount of an object betweenthese pictures according to the principle of triangulation and producesdistance images presenting three-dimensional distance distribution.Furthermore, the obstacle recognition section 15 b makes image processessuch as extracting a feature of a box-like pattern from the distanceimages, identifies an object existing ahead of an own vehicle as anobstacle from thus obtained solid objects and detects a distance L_(r)between the obstacle and the own vehicle, a relative traveling speedV_(r) of the obstacle versus the own vehicle and a width W of theobstacle. The distance L_(r) and the relative speed V_(r) are outputtedto the deceleration judging section 15 c, the deceleration calculatingsection 15 d, the braking distance judging section 15 f and the firstyaw rate calculating section 15 g and the width W is outputted to thefirst yaw rate calculating section 15 g. That is, the pair of the CCDcameras 11 and the obstacle recognition section 15 g form an obstaclerecognition means.

[0024] According to the first embodiment, the deceleration judgingsection 15 c compares the distance L_(r) with a threshold distanceL_(lmt) which has been memorized beforehand and judges whether or notthe distance L_(r) is smaller than the threshold distance L_(lmt). Theresult of judgment is outputted to the deceleration calculating section15 d.

[0025] When the distance L_(r) becomes smaller than the thresholddistance L_(lmt) (L_(r) L_(lmt)), the deceleration calculating section15 d calculates a road gradient θ _(SL) according to a formula (1) shownbelow and calculates an automatic braking deceleration a which is atarget deceleration according to the relative speed Vr and the roadgradient θ_(sL). The established automatic braking deceleration α_(s) isoutputted to the brake control section 15 e.

[0026] The road gradient θ^(SL) (%) is expressed as follows:

θ_(SL)=(Gx−rate of change of vehicle velocity)/g100  (1)

[0027] where Gx is longitudinal acceleration (m/s²) and g isgravitational acceleration (m/s²). The road gradient θ_(SL) (%) may becalculated from an engine output torque (N−m), a torque ratio of atorque converter (in case of an automatic transmission vehicle), a gearratio of a transmission, a final reduction gear ratio, a tire radius(m), a running resistance (N), a vehicle weight (kg), a change of rateof vehicle velocity (m/s²) and gravitational acceleration (m/s²). Also,the road gradient θ_(SL) may be obtained from altitude data of anavigation apparatus or may be obtained from road configuration dataprepared based on image data of a CCD camera.

[0028] The automatic braking deceleration α_(s) is established at alarger value as the relative velocity Vr is high. This is because as therelative velocity is high, a larger deceleration is needed in order tomake the relative velocity nil. Further, the automatic brakingdeceleration α_(s) is established at a large value in order to preventdeceleration from becoming too low in case where the road gradientθ_(SL) is a down-grade and is established at a small value in order toprevent deceleration from becoming too high in case where the roadgradient θ_(SL) is an up-grade. The automatic braking deceleration α_(s)may be calculated by multiplying a predetermined constant by a constantvariably established according to the relative velocity V_(r) or theroad gradient θ_(SL) or may be established from a map parameterizing therelative velocity V_(r) and the road gradient θ_(SL). Further, in thisembodiment, the automatic braking deceleration α_(s) is designed to beestablished according to the relative velocity Vr and the road gradientθ_(SL), however this automatic braking deceleration α_(s) may beestablished only by the relative velocity depending upon the vehiclemodel, vehicle specifications and other conditions or may be establishedonly by the road gradient θ_(SL) or may be a fixed value.

[0029] The brake control section 15 e receives a signal of automaticbraking deceleration α_(s) from the deceleration calculating section 15d or a signal of target braking force FB which will be describedhereinafter and a signal of a selected wheel for braking from theautomatic brake control section 15 j and outputs a signal of brake fluidpressure corresponding to those inputted signals to the brake drivesection 1.

[0030] The braking distance judging section 15 f inputs a signal ofactual deceleration a_(x) from the longitudinal acceleration sensor 8,signals of distance L_(r) and relative velocity V_(r) from the obstaclerecognition section 15 b and a signal of automatic braking decelerationa from the deceleration calculating section 15 d and judges whether ornot the vehicle can continue deceleration without contacting an obstacleahead of the own vehicle.

[0031] This judgment is made by comparing the distance L_(r) with abraking distance (V_(r) ²/(2a_(x)))obtained from the relative velocityV_(r) and the actual deceleration a_(x). In case where the distanceL_(r) is smaller than the braking distance (V_(r) ²/(2a_(x)) ), it isjudged that the vehicle will contact the obstacle before thedeceleration is completed and in case where the distance L_(r) is largerthan the braking distance (V_(r) ²/(2a_(x))), it is judged that thedeceleration

[0032] will be completed without contacting the obstacle. The result ofthe judgment is outputted to a first yaw rate calculating section 15 gand a second yaw rate calculating section 15 h, respectively. Thebraking distance judging section acts as a braking distance judgingmeans.

[0033] The first yaw rate calculating section 15 g receives signals ofthe actual deceleration ax from the longitudinal acceleration sensor 8,the vehicle speed V from the vehicle speed calculating section 15 a, thedistance L_(r) from the obstacle recognition section 15 b, the relativevelocity V_(r) and the width W of the obstacle and calculates a yaw rate(hereinafter referred to as “first yaw rate γ₁”) required for turningaround the obstacle ahead based on these data. That is, this first yawrate calculating section 15 g acts as a first parameter calculatingmeans. The calculated first yaw rate γ₁ is outputted to the target yawrate establishing section 15 i.

[0034] Specifically, the first yaw rate γ₁ is calculated according tothe following formula (4).

[0035] First, a time T_(a) required for the vehicle to reach theobstacle is expressed as;

T _(a)=(V _(r)−(V _(r) ²−2·a _(x))^(1/2)) /a _(x)  (2)

[0036] A lateral acceleration a_(y) required for the vehicle to move inthe lateral direction is expressed as;

a _(y)=2·W/T _(a)  (3)

[0037] the first yaw rate γ₁ required to obtain the lateral accelerationa_(y) is expressed as;

γ₁=a_(y) /V  (4)

[0038] The second yaw rate calculating section 15 h is for calculating ayaw rate currently generating as a second yaw rate γ₂. The second yawrate calculating section 15 h receives a signal of a steering wheelangle θ_(H) from the steering wheel angle sensor 7, and a signal of thevehicle speed V from the vehicle speed calculating section 15 a andcalculates the second yaw rate γ₂. The second yaw rate calculatingsection 15 h acts as a second parameter calculating means. Thecalculated second yaw rate γ₂ is outputted to a target yaw rateestablishing section 15 i.

[0039] Specifically, the second yaw rate γ₂ is calculated according tothe following formula (5):

γ₂=1/(1+T·S)·γ_(t0)  (5)

[0040] where S is Laplace operator; T is first-order lag time constant;and γ_(t0) is yaw rate stationary value.

[0041] Further, first-order lag time constant T is obtained from thefollowing formula (6):

T=(m·L _(f) ·V)/(2·L·K _(r))  (6)

[0042] where m is vehicle weight; L is wheel base; L_(f) is distancebetween front axle and center of gravity and k_(r) is rear equivalentcornering power.

[0043] Further, the yaw rate regular value γ_(t0) is given by thefollowing formula (8):

γ_(t0) =Gγδ·(θ_(H) /n)  (7)

[0044] where Gγδ is yaw rate gain; n is gear ratio of steering gear andθ_(H) is

[0045] On the other hand, yaw rate gain G γδ is obtained from thefollowing formula (8):

Gγδ=1/(1+A·V ²)·(V/L)  (8)

[0046] where A is stability factor which is determined by vehiclespecifications and is calculated from the following formula (9):

A=−(m/(2·L ²)) ·(L _(f) ·K _(f) −L _(r) ·K _(r))/(K _(f) ·K _(r))  (9)

[0047] where L_(r) is distance between rear axle and center of gravityand K_(f) is front equivalent cornering power.

[0048] The target yaw rate establishing section 15 i receives a signalof first yaw rate γ₁ from the first yaw rate calculating section 15 gand a signal of second yaw rate γ₂ from the second yaw rate calculatingsection 15 h and establishes a larger one of these as a target yaw rateγ_(t). The target yaw rate establishing section 15 i acts as a targetyaw rate establishing means in the present invention.

[0049] The automatic brake control section 15 j controls brakes ofrespective wheels so as to generate a turning force over the vehicle.First, the automatic brake control section 15 j outputs signals of atarget braking force FB and a selected object wheel to the brake controlsection 15 e. Then, the brake control section 15 e outputs a signal ofbrake fluid pressure corresponding to these signals to the brake drivesection 1 to generate a turning force in the vehicle. That is, in thepresent invention, the automatic brake control section 15 j, the brakecontrol section 15 e and the brake drive section 1 constitute anautomatic brake control means and a vehicle behavior control means.

[0050] For example, as the applicant of the present invention proposesin Japanese Patent Application Laid-open No. Toku-Kai-Hei 10-157589, theautomatic brake control section 15 j establishes a target braking forceand a selected object wheel and outputs these signals to the brakecontrol section 15 e.

[0051] The automatic brake control section 15 j inputs a steering wheelangle θ_(H) from the steering wheel angle sensor 7, a lateralacceleration G_(y) from the lateral acceleration sensor 9, a vehiclespeed V from the vehicle speed calculating section 15 a and a target yawrate γ_(t) from the target yaw rate establishing section 15 j,calculating a target yaw moment M_(z) based on these, and obtains atarget braking force FB according to the following formula (10).

FB=M _(z)/(d/2)  (10)

[0052] where d is tread of a vehicle.

[0053] The turning direction of the vehicle is judged by an actual yawrate from the yaw rate sensor 10. When the calculated target momentM_(z) has the same turning direction as the actual yaw rate, a rearinner wheel of the turning circle is selected as an object wheel towhich the braking force is applied. When the target moment M_(z) has anopposite turning direction to the actual yaw rate, a front outer wheelof the turning circle is selected as an object wheel to which thebraking force is applied. Specifically, the following combination isestablished beforehand. With respect to the direction of moments, actualyaw rate γ and target yaw moment M_(z), the left turn denotes positive(+) and the right turn denotes (−).

[0054] In order to judge a straight line running condition of thevehicle, ε is established as a positive number close to zero which hasbeen obtained from experiments or calculations beforehand. To judge thatthe target yaw moment M_(z) is approximately zero, εM_(z) is establishedas a positive number close to zero which has been obtained fromexperiments or calculations.

[0055] Case 1: when γ>ε and M_(z)>MεM_(z) left rear wheel braked

[0056] Case 2: when γ>ε and M_(z)<−εM_(z) right front wheel braked

[0057] Case 3: when γ<ε and M_(z)>εM_(z) left front wheel braked

[0058] Case 4: when γ<ε and M_(z) <−εM_(z) left rear wheel braked

[0059] Case 5: when the vehicle in approximately straight line runningcondition of |γ|≦ε or when the vehicle is turning condition of M_(z)≦εM_(z) no brake applied to any wheel

[0060] Next, an operation of thus constituted motion control system willbe described by reference to a flowchart of FIG. 3. This flowchart isrepeatedly executed every specified time. First, at a step (hereinafterreferred to as just “S”) 101, signals from sensors 6, 7, 8, 9, 10 and asignal from the pair of CCD cameras are read. Particularly, the vehiclespeed V in the vehicle speed calculating section 15 a, the distanceL_(r) to an obstacle, the relative velocity V_(r) the width of theobstacle in the obstacle recognition section 15 b and other necessaryparameters are detected and the program goes to S102.

[0061] At S102, in the deceleration judging section 15 c, the distanceLr is compared with the threshold distance L_(lmt) memorized. In casewhere the distance L_(r) is smaller than the threshold distance L_(lmt)(L_(r)≦L_(lmt)), the program goes to S103 and in case where the distanceL_(r) is larger than the threshold distance L_(lmt) (L_(r)>L^(lmt)), theprogram leaves the routine.

[0062] As a result of the comparison at S102, when the program goes toS103, the deceleration calculating section 15 d calculates a roadgradient θ_(SL) according to the formula (1) and calculating a targetdeceleration according to the relative speed Vr and the θ_(SL),establishing the deceleration as an automatic braking decelerationα_(s), and outputs the deceleration to the brake control section 15 e.

[0063] Then, the program goes to S104 where the brake control section 15e outputs a signal of fluid pressure according to the automatic brakingdeceleration α_(s) to the brake drive section 1.

[0064] After that, the program goes to S105 where the actualdeceleration a_(x) detected by the longitudinal acceleration 8 is readand then goes to S106.

[0065] At S106, in the braking distance judging section 15 f, thedistance L_(r) is compared with the braking distance (V_(r) ²/(2·a_(x)))until deceleration is completed. Further, in case where the distanceL_(r) is smaller than the braking distance (V_(r) ²/(2·a_(x))), it isjudged that the vehicle can not complete deceleration without contactingthe obstacle ahead and the program goes to S107. On the other hand, incase where the distance L_(r) is larger than the braking distance (V_(r)²/(2·a_(x))), it is judged that the vehicle can complete decelerationwithout contacting the obstacle ahead and the program leaves theroutine.

[0066] When the program goes to S107 as a result of the judgment thatthe vehicle can not complete deceleration without contacting theobstacle ahead, based on the actual deceleration a_(x), the relativespeed V_(r), the distance L_(r) and the width W, the first yaw ratecalculating section 15 g calculates the first yaw rate γ₁ necessary foravoiding the obstacle by a turn according to the formula (4).

[0067] Next, the program goes to S108 where the second yaw ratecalculating section 15 h calculates the second yaw rate γ₂ based on thesteering wheel angle θ_(H) and the vehicle speed V according to theformula (5).

[0068] After that, the program goes to S109 where in the target yaw rateestablishing section 15 i an absolute value |γ₁| of the first yaw rateγ₁ is compared with an absolute value |γ₂| of the second yaw rate γ₂. Incase where the absolute value |γ₁| of the first yaw rate γ₁ is smallerthan the absolute value |γ₂| of the second yaw rate γ₂, that is,|γ₁|<|γ₂|, the program goes to S110 where since the vehicle can avoidcontacting the obstacle with the present running conditions retained,the target yaw rate γ_(t) is established at the second yaw rate γ₂.Further, in case where the absolute value |γ₁| of the first yaw rate γ₁is larger than the absolute value |γ₂| of the second yaw rate γ₂, thatis, |γ₁|≧|γ₂|, the program goes to S111 where the target yaw rate γ_(t)is established at the first yaw rate γ₁ to avoid the obstacle.

[0069] After thus the target yaw rate γ_(t) is established, the programgoes to S112 where the automatic brake control 15 j calculates thetarget moment M_(z) based on the steering wheel angle θ_(H), the lateralacceleration G_(y) , the vehicle speed V and the target yaw rate γ_(t)and based on the target moment M_(z) the target braking force FB iscalculated. Further, based on the actual yaw rate γ and the target yawmoment M_(z), the wheel to be braked is selected. Thus, the vehiclebehavior control is formed.

[0070] According to the first embodiment, in case where the avoidance ofcontacting the obstacle is inadequate only with deceleration, a turningforce is given to the vehicle by applying brake to the selected wheel,thereby the vehicle can surely avoid contacting the obstacle.

[0071] In this embodiment, the function of the automatic brake controlsection 15 j is described citing an example of the braking force controlapparatus proposed in Toku-Kai-Hei 10-157589, however other examples maybe applied to the automatic brake control section according to thepresent invention.

[0072] Next, a second embodiment will be described by reference to FIGS.4 and 5. According to the second embodiment, the vehicle behaviorcontrol means comprises a rear wheel steering control means forautomatically steering rear wheels.

[0073] As shown in FIG. 5, the vehicle is equipped with a rear wheelsteering section 20. The rear wheel steering section 20 is provided witha rear wheel steering motor 21 which is controlled by a rear wheelcontrol section 25 a of a control unit 25. A power of the rear wheelsteering motor 21 is transmitted through a worm and worm gear and a linkmechanism to the left rear wheel 4rl and the right rear wheel 4rrrespectively to steer these rear wheels.

[0074] Further, the control unit 25 comprises the vehicle speedcalculating section 15 a, the obstacle recognition section 15 b, thedeceleration judging section 15 c, the deceleration calculating section15 d, the brake control section 15 e, the braking distance judgingsection 15 f, the first yaw rate calculating section 15 g, the secondyaw rate calculating section 15 h, the target yaw rate establishingsection 15 i and the rear wheel steering control section 25 a. In thisembodiment, the automatic brake control section 15 j is replaced withthe rear wheel steering control section 25 a.

[0075] In the rear wheel steering control section 25 a, a rear wheelsteering angle γ_(r) is established by the following formula (11):

δ_(r) =k·γ _(t)  (11)

[0076] where k is a constant predetermined.

[0077] When the target yaw rate γ_(t) is inputted from the target yawrate establishing section 15 i, the rear wheel steering control section25 a drives the rear wheel steering motor 21 such that the rear wheelshave a steering angle corresponding to the inputted target yaw rateγ_(t), respectively, and as a result a turning force is generated in thevehicle.

[0078] Thus, according to the second embodiment, in case where thevehicle can not avoid contacting an obstacle ahead only withdeceleration, an automatic steering of rear wheels generates a turningforce in the vehicle, thereby the vehicle can surely avoid contactingthe obstacle.

[0079] Further, in the second embodiment, the rear wheel steeringcontrol section 25 a makes a steering control according to a yaw rateproportional method, however other methods may be employed. Further, ahydraulic actuator may be used for the rear wheel steering motor 21.

[0080]FIGS. 6 and 7 shows a third embodiment of the present invention.According to the second embodiment, the vehicle behavior control meansconsttutes a front wheel steering control means for automaticallysteering front wheels.

[0081] Referring to FIG. 7, reference numeral 30 denotes a front wheelsteering section for automatically steering front wheels and referencenumeral 31 denotes a front wheel steering motor whose power istransmitted to the left front wheel 4fl and the right front wheel 4frthrough a worm and worm wheel and a link mechanism.

[0082] Further, a control unit 35 comprises the vehicle speedcalculating section 15 a, the obstacle recognition section 15 b, thedeceleration judging section 15 c, the deceleration calculating section15 d, the brake control section 15 e, the braking distance judgingsection 15 f, the first yaw rate calculating section 15 g, the secondyaw rate calculating section 15 h, the target yaw rate establishingsection 15 i and the front wheel steering control section 35 a. Theautomatic brake control section 15 j of the first embodiment is changedto the front wheel steering control section 35 a.

[0083] When the front wheel steering control section 35 a inputs atarget yaw rate γ_(t), a front wheel steering angle δ_(r) is calculatedaccording to the following formula (12):

δ_(r)=(1+T·S)·_(t) /G γ _(t) /G γδ  (12)

[0084] Then, the front wheel steering control section 35 a rotates thefront wheel steering motor 31 by the displacement necessary to obtainthe front wheel steering angle δ_(r). That is, according to the thirdembodiment, when the target yaw rate γ_(t) is inputted from the targetyaw rate establishing section 15 i, the front wheel steering controlsection 35 a drives the front wheel steering motor 31 so as to obtain arequired front wheel steering angle, and as a result a turning force isgenerated in the vehicle.

[0085] Thus, according to the third embodiment, in case where thevehicle can not avoid contacting an obstacle ahead only withdeceleration, an automatic steering of front wheels generates a turningforce in the vehicle, thereby the vehicle can surely avoid contactingthe obstacle.

[0086] In the aforesaid embodiments of the present invention, the targetyaw rate calculated from the first yaw rate and the second yaw rate isused as a parameter needed for moving the vehicle in the lateraldirection, however, alternatively, a lateral acceleration calculatedfrom a first lateral acceleration and a second lateral acceleration isused for calculating a target lateral acceleration and based on thistarget lateral acceleration the vehicle behavior may be controlled.

[0087] Further, the automatic brake control means in the firstembodiment, the rear wheel steering control means in the secondembodiment, and the front wheel steering control means in the thirdembodiment are the vehicle behavior control means for laterally movingthe vehicle independently, respectively. However, the vehicle behaviorcontrol means may be constituted by the combination of a plurality ofthese control means.

[0088] While the presently preferred embodiments of the presentinvention have been shown and described, it is to be understood thatthese disclosures are for the purpose of illustration and that variouschanges and modifications may be made without departing from the scopeof the invention as set forth in the appended claims.

What is claimed is:
 1. A motion control system of an own vehicle havingan obstacle recognition means for detecting an obstacle in front of thevehicle and for obtaining an information of the obstacle and a runningcondition detecting means for detecting running conditions of thevehicle, comprising: a braking distance judging means for when adeceleration is applied to said vehicle judging whether or not saidvehicle can finish said deceleration without contacting said obstaclebased on said information of said obstacle and said running conditions;a first parameter calculating means for calculating a first parameternecessary to take a lateral avoidance motion based on said obstacleinformation and said running conditions; a second parameter calculatingmeans for calculating a second parameter representing a parameterpresently generating in said vehicle based on said running conditions; atarget parameter establishing means for when it is judged that saidvehicle can not finish said deceleration without contacting saidobstacle, establishing a target parameter by comparing said firstparameter with said second parameter; and a vehicle behavior controlmeans for generating said lateral avoidance motion of said vehicle atleast in accordance with said target parameter.
 2. The motion controlsystem according to claim 1 , wherein said first parameter is either ayaw rate or a lateral acceleration.
 3. The motion control systemaccording to claim 1 , wherein said second parameter is either a yawrate or a lateral acceleration.
 4. The motion control system accordingto claim 1 , wherein said vehicle behavior control means is at least oneof an automatic brake control means for braking a selected wheel togenerate a turning force, a rear wheel steering control means forautomatically steering a rear wheel and a front wheel steering controlmeans for automatically steering a front wheel.